ISHS Acta Horticulturae 819: International Symposium on Growing Media 2007
DEVELOPMENT OF A RAPID AND ACCURATE DETERMINATION OF PARTICLE SIZE DISTRIBUTION IN ORGANIC SUBSTRATES |
| Authors: | M.R. Nemati, J.P. Fortin, M.C. Lussier, M.J. Prince |
| Keywords: | growing media, peat, physical properties, dry sieving, wet sieving, decomposition degree of substrate |
| Abstract:
Knowledge of particle size distribution (PSD) is essential to formulating growing media and also for monitoring their properties during manufacturing. The objectives of this study were first to evaluate the role of various parameters on PSD determination, and then to develop a rapid and accurate method for determination of PSD in organic substrates. A laboratory study was conducted on several peat-based substrates with different degrees of decomposition. The impact of the initial volume of the sample, the substrate water content, the degree of substrate decomposition and the duration of sieving on PSD were evaluated. The results show that the degree of decomposition of the substrate considerably affects the PSD and hence the method of analysis must be adopted according to the degree of decomposition. For less decomposed substrates (blond peat), dry sieving is highly recommended. In this study, a rapid dry sieving method for determining PSD was developed using accelerated drying in a microwave oven. The results showed that this method takes approximately 15 min. for an accurate measurement, which is significantly faster than all other existing methods. The optimal parameters for an accurate and reproducible PSD determination using dry sieving were also determined. These parameters were about 250-ml of a sample with a moisture content of 15 to 20% (w/w) and a sieving period of 6 min. For more decomposed materials (e.g. black peat, brown peat) in which dry sieving cannot produce an adequate degree of separation between the primary particles, use of the wet sieving method is more appropriate. According to this study, the development of a set of international standards is highly desirable for determining the particle size distribution in order to produce comparable results. | |
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